Loud-speaker



Patented July 16, w29.

UNiTED stares N F F ECE.

RICHARD FRENKEL, 0F BERLIN-GRUNEWALD, GERMANY.

LOUD-SPEAKER.

Application led April 1G, 1926, Serial No. 102,539, and in Germany April17, 1925.

This invention relates to devices for reproducing sound by the aid of adiaphragm, such as sound boxes vfor gramophones and the like, receiversfor telephones, Wireless apparatus and so forth.

The invention comprises in combination with a diaphragm adapted to bevibrated mechanically or electromagnetically, a second diaphragm ormembrane stretched substantially parallel with the first at a shortdistance from it. The invention also comprises the severalconstructions, means of atttaching and tensioning diaphragms, andconformations of sound box described hereinafter.

Examples of loud speakers constructed in accordance with the inventionare illustrated in axial section in the accompanying drawings.

Figure 1 shows one form or embodiment of my invention; Fig. 2 is asimilar structure to Fig. 1 but constituting an improved form thereof;Fig. 3 is another embodiment of the invention similar to Fig. 1; .andrig. 4 is an improvedy form of the structure shown in Fig. 3.

In all the constructions illustrated there is a case l, which in anelectromagnetically opcrated instrument contains an electromagnet 2.Adjacent the poles of this is a diaphragm 3, which ordinarily is ofmagnetic material to co-act with the magnet; this closes the mouth ofthe case. Near the diaphragm 3 and substantially parallel with it thereis mounted a second diaphragm or membrane 4. 'l` his mav consist of athin sheet of metal foil, paper or the like; metal foil of from .001 tol m. in. has been found suitable, and a membrane consisting of copperfoil tinned or varnished gives a pleasant soft tone. The two diaphragmsare separated by the ring 5. The diaphragms are secured in place by acover 6. which may be fastened in any suitable way to the case 1, as byscrews passing through its edge and the flange of the case as indicatedin Figure 4. In the cover 6 there is a sound openingr 8, generallyformed with a tubulure for the attachment of a horn or trumpet.

In the construction of Figure 1 the outer part of ring 5 is of lessthickness than the inner part, and the flange 7 of the cover 6 is shapedto conform to it. Consequently when the flange is drawn down upon thering by the fastening means, the diphragm 4 is-both gripped andtensioned. The inner surface of the cover 6 in Figure 1 is flat andsubstantially parallel with the diaphragms.

, In the construction of Figure 2 the space above the dia hragm 4 isconical. To produce this resu t a ring 9 is inserted between the cover 6and the diaphragm 4, said ring having a conical interior surface.Alternatively as indicated in Figure 3 the cover 6 itself may beconical, or have a conical interior surface. This conformation of thespace between the diaphragms and the sound opening has been found toproduce more natural tones. The conical surface may be straight lines orcurves of any desired shape.

In the construction of Figure 3 the Aring 5 is made of rubber or other'soft and compressible materal. The cover 6 is formed with annular ribs10 which extend into the soft ring 5 and thereby bring about thetensioning of the diaphragm 4 substantially as described with referenceto Figure 1.

In the construction of Figure 4 the ribs 10 integral with the coverarereplaced by independent rings 11, for instance of wire, whichsimilarly ress the diaphragm 4 into the soft ring 5 and) thereby tensionit.

What I claim is 1. In combination a casinof having an opening of smallarea compared with the crosssection of said casing, two diaphragmsextending across said casing parallel with one another and a shortdistance apart, one of said diaphragms being of magnetic material andthe other of said diaphrafrms being of thin metallic foil and means forvibrating said ma etic diaphragm for imparting corresponding vibrationsto said thin metallic foil diaphragm.

2. A loud speaking telephone comprising a casing, a magnetic diaphragmsecured in said casing, an electro-magnet 1n said casing adjacent saiddiaphragm, a sheetlike diaphragm fastened in said casing substantiallyparallel with said magnetic diaphragm and means extending from saidcasing for stretching said sheet-like diaphragm in radial directions. v

3. A device for reproducing sound comprising a case, a diaphragm closingthe mouth of said case, means for vibrating said daphragm, a ringdisposed upon said diav phragm, a membrane stretched over said ringtioned diaphragm, and means fastening and tensioning said membrane inposition between said case and said ring.

4. A device for reproducing sound, comprising a circular casing havingan opening substantially smaller in diameterthan the diameter of saidcasing and a coned interior surface adjacent said casing, a membranestretched across the base of said coned surface a diaphragm positionedparallel with said membrane at a short distance therefrom, and means forimparting vibrations to said diaphragm.

5. A device for reproducing sound comprising a iianged case, a diaphragmclosing the mouth of said case, means for imparting vibrations to saiddiaphragm, an annular casing ring resting upon the edge of saiddiaphragm, a membrane upon said ring, a cover adapted to engage saidring and means interposed between said cover and said spacer ring fortensioning said membrane.

6. A loud speaker comprising a casing, a diaphragm extending across saidcasing, means for vibrating said diaphragm, a second very thin diaphragmstretched across said casing and a exible member spacing one of saiddiaphragms substantially parallel to and 'at a short distance from theiii-st.

7. A loud speaker comprising a casing, a

diaphragm extending across said casing, means for Vibratin saiddiaphragm, and a second very thin diaphragm of tinned co per sheetstretched across said casing su stantially parallel toand at a shortdistance from thefirst.

8. A loud speaker comprising a casing, a

diaphragm extending across 1said casing, means for vibrating said diahragm, and a second very thin diaphragm o japanned copper sheetstretched across said casing substantially parallel to and at a shortdistance from the rst.

9. A sound reproducer comprising an electromagnetic actuating mechanism,a diaphragm driven by said mechanism, a casing enclosing said mechanismand forming an annular support for said diaphragm, a resilient ringmember concentrically positioned with respect to said annular support, ametallic foil sheet, and means on said casingpfor pressing said sheetagainst said resilient ring member and stretching said sheet in a planeparallel to the plane of said diaphragm for establishing a chamberbetween said diaphragm and sheet and-securing sound reproduction fromboth said diaphragm and sheet.

ln testimony whereof 1 have signed my name to this specification.

RICHARD FRENKEL.

